Go for it! I know that there is a chili called the Rocopica, which is a cross between an Ulupica and a Rocoto. From what I've read (because I can't seem to get my Ulupica seeds to sprout!!!) the Rocopica is bigger than the Ulupica (which resembles a Chiltepin), but retains the flavor of the Ulupica. Of course, I haven't had the pleasure of testing this out myself.
As far as making the Chiltepin bigger, one of the characteristics that makes the Chiltepin such a special chili is its size. Here in Southern Arizona, especially among the Latino Community, Chiltepins are a favorite and fetch a high price when available. Many households and restaurants have jars of dried chiltepins on the table so that an individual can add one or more to their soup or meal. For many people, one crushed Chiltepin is enough for their taste. Those who like it a bit hotter might do two or three Chiltepins.
Dustin, I picked 266 fresh Chiltepins this past November and spent three days de-seeding them all. I couldn't use gloves, because they made it difficult to break open for retrieving the seeds. I saved the hulls with whatever pulp was left, let them dry, and I still use these hulls with pulp (very tasty). However, I can tell you from personal experience that a Chiltepin is pretty much a skin with very little pulp, and the vast majority of the pepper being seed. The average number of seeds I got from each Chiltepin I de-seeded (Yes, I tracked it) was 17 seeds. In other words, a Chiltepin is almost all seed surrounded by a thin skin.
I'm curious as to why it would be difficult to make hot sauce from Chiltepins due to their size. I don't know what your recipe is or will be, but I guarantee you that you'll soon discover that attempting to remove the seeds and only using the "pulp" will be a major effort with disappointing results. My favorite hot sauces are Chiltepin hot sauces I buy down in Nogales, Sonora, and they all have seeds in them. If you plan to use the whole Chiltepin, then don't worry about their size. They are easy to pick. You don't have to use scissors.
I hope this helps a little.